The Return of the King, LoTR Appendix B, The Tale of Years: The Third Age

... Thráin stood before them. ... he said: 'Good! We have the victory. Khazad-dûm is ours!' ...

'No,' said Dáin. 'You are the father of our Folk, and we have bled for you, and will again. But we will not enter Khazad-dûm. You will not enter Khazad-dûm. Only I have looked through the shadow of the Gate. Beyond the shadow it waits for you still: Durin's Bane. The world must change and some other power than ours must come before Durin's Folk walk again in Moria.'